如何从MySQL表中选择列为NULL的数据

本文介绍了如何从MySQL表中选择列为NULL的数据的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我希望下面的代码向我显示表中交换列为null但结果集显示0行的所有记录.知道为什么吗?

I expect the following code to show me all the records in the table where the exchange column is null but the result set show 0 rows. Any idea why?

SELECT * FROM pubco WHERE exchange IS NULL;

推荐答案

也许您已将''解释为NULL，但这并不相同，请尝试

maybe you have interpreted '' as NULL which is not the same, but try this

SELECT * FROM pubco WHERE exchange IS NULL OR exchange = ''

但是如果仍然没有获得值，也许它上面有空格，所以您应该TRIM它，

but if still not getting the value, maybe it has spaces on it, so you should TRIM it,

SELECT * FROM pubco WHERE exchange IS NULL OR TRIM(exchange) = ''